This invention relates to the field of ink jet printheads and in particular, to printheads having enhanced corrosion protection.
Ink jet printheads contain semiconductor chips which are electrically activated to eject ink droplets on demand through nozzle holes in a nozzle plate attached to the chips. In a xe2x80x9croof shooterxe2x80x9d type printhead, ink is provided to the active surface of the chips for ink droplet ejection through ink vias or ink feed slots formed through the thickness dimension of the silicon chips. The ink ejection devices are typically located in close proximity to the ink feed via or slot along opposing sides thereof for the length of the ink feed via or slot. Metal conducting traces or lines are provided on the chip adjacent the ink feed slots to provide power to the ink ejection devices. Because of the corrosive nature of the ink, the ink ejection devices and metal traces should be protected from the ink. A variety of layers of protective material may be used to provide protection against corrosion for the ink ejection devices and metal conducting layers. However, despite the use of protective layers over the ejection devices and metal layers, ink often gets between the nozzle plate and a planarizing layer on the chip causing delamination between the nozzle plate and planarizing layer. Once delamination has occurred, the ink may find its way to the chip surface thereby corroding unprotected metal conducting layers. There is a need therefore for improved methods for protecting the metal conducting layers on an ink jet chip from ink corrosion and damage.
The foregoing and other needs are provided by a method for reducing ink corrosion of exposed metal layers on a chip surface of a semiconductor chip for an ink jet printhead, the chip having an elongate ink feed via and ink ejectors adjacent the ink feed via. The method includes depositing a protective layer in a plasma process to the chip surface, the protective layer being deposited adjacent the ink ejectors so that the protective layer substantially circumscribes the ink via. A thick film layer is applied to the protective layer and chip, whereby the protective layer and thick film layer are sufficient to promote increased adhesion between the thick film layer and a nozzle plate attached to the thick film layer thereby substantially reducing a tendency for the nozzle plate and thick film layer to delaminate from one another during printhead manufacture or use and interrupting contact between ink and the exposed metal layers on the chip surface.
In another aspect the invention provides a semiconductor chip for an ink jet printhead, the chip having a chip surface, an elongate ink via therein, ink ejectors on the chip surface adjacent the ink via, metal conductive traces attached to the ink ejectors and a protective layer deposited adjacent the ink ejectors. The protective layer substantially circumscribes the ink via and provides an improved seal between a thick film layer and a nozzle plate attached to the thick film layer sufficient to inhibit delamination and ink flow between the thick film layer and the nozzle plate.
An important aspect of the invention is that the protective layer extends completely around the ink via region thereby forming a seal xe2x80x9cringxe2x80x9d for improved adhesion of the thick film layer to the nozzle plate. The protective layer is advantageously wide enough to reduce instances of delamination between the nozzle plate and thick film layer and subsequent ink corrosion of exposed metal outside of the seal ring area. Because the seal ring may be deposited by typical semiconductor processing techniques, an improved adhesion between the nozzle plate and the thick film adjacent the ink via area may be provided without resorting to exotic adhesives or other multi-step methods for improving adhesion. Furthermore, the width of the seal ring may be easily adjusted to provide more or less adhesion promotion surface.